The present invention relates generally as indicated to an antenna and, more particularly, to an antenna element that has a stripline feed and can be easily incorporated into low cost, light weight antenna arrays.
An antenna system can comprise an array of antenna elements arranged, for example, in eight two-by-two arrays. One form of an antenna element, commonly called a patch antenna, comprises a planar patch of conductive material that serves as its radiating component. Patch antennas have traditionally been viewed as being inexpensive to manufacture and as being easily incorporated into low cost, light weight antenna arrays.
In a patch antenna element, the conductive patch is formed on a dielectric layer by, for example, etching, and other known techniques usually requiring skilled touch labor. The dielectric layer supports the patch and positions it parallel to a conductive ground plane and a feed is provided to communicate electromagnetic energy to or from the patch. Typically, the ground plane and the feed will be part of a stripline circuit positioned under the patch and its supporting dielectric layer.
A stripline circuit usually comprises a compilation of boards press-bonded or otherwise joined together. The outer surface of each of dielectric boards has a conductive coating (e.g., copper cladding) thereon and plated vias between the conductive coatings and through the dielectric boards. A conductive feedline is formed on one board""s inner surface. With a coaxial connection, the outer conductor is connected to one of the conductive coatings and the inner conductor is connected to the feedline which in turn is electrically connected to the patch.
The electrical connection between the patch and the stripline feed can be accomplished by a coaxial-coupling pin welded to the patch and extending through the patch""s supporting layer and the adjacent stripline layer, with appropriate insulation provided in the conductive coating, to the feed. In an antenna system comprising eight two-by-two arrays, thirty-two pins, welds, aligned openings, and insulated passages would be necessary. These pins can be replaced by coupling slots, provided that the slot is bent or otherwise configured to be longer than the patch and that the slot does not cause spurious radiation.
The present invention provides a xe2x80x9cpatchlessxe2x80x9d antenna element that is just as easily incorporated into an antenna array as a conventional patch antenna element. The antenna element can be constructed without coaxial coupling pins and without patch radiators (and the corresponding support layer). The elimination of these conventionally necessary components greatly reduces antenna cost, weight and/or packaging. The antenna element can generate circular polarization thereby resulting in higher efficiency and greater circular polarization bandwidth.
More particularly, the present invention provides an antenna element comprising a first conductive plane, a second conductive plane, and one or more dielectric layers separating the first and second conductive planes. A resonant cavity is formed by a portion of the first conductive plane, a portion of the second conductive plane, and electrical connections (e.g., plated vias) extending therebetween. A slot is formed in the portion of the second conductive plane forming one side of the resonant cavity and the feedline extends into the cavity. In this manner, a field can be set in the cavity when excited by the feedline and electromagnetic signals coupled to or from the resonant cavity. The central conductor of a coaxial coupling can be connected to the feedline and its outer conductor can be connected to the first conductive plane.
An antenna array can incorporate a plurality of the antenna elements according to the present invention. Such an antenna array can be made by compiling a plurality of boards and extending electrical connections (e.g., plated vias) therebetween. A first board would be made of a dielectric material and have a first conductive coating on one surface and a second board would also be made of a dielectric material and have a second conductive coating on one surface. Slots would be formed in the second conductive coating and a feedline circuitry would be printed on the opposite surface of the second board. The first conductive coating would form the first conductive plane for each of the antenna elements, the second conductive coating would form the second conductive plane for each of the antenna elements, and the feedline circuitry would include the feedline for each of the antenna elements.
The present invention provides these and other features hereinafter fully described and particularly pointed out in the claims, the following description and annexed drawings setting forth in detail a certain illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principles of the invention may be employed.